MECHANICS AND USEFUL ARTS. 61 



(Blake's patent), I have often heard it asserted, by mill owners and others, 

 that water-wheels will do more work in the night than in the daytime. To 

 demonstrate the fallacy of such an assertion by actual and scientific experi- 

 ments, I have, with great care and with the use of every perfect apparatus 

 for testing water-wheels, observed their performance in several successive 

 days and nights, namely, five experiments in the middle of the day and 

 three in the middle of the night, on a wheel of 18 inches in diameter, run- 

 ning without resistance under a fall (H) of eight and more feet; running the 

 wheel for 2000 revolutions at each experiment; and the time being calcu- 

 lated by noting the sounds for every 100 revolutions, by the bell-hammer 

 attached to the wheel-shaft, which is a good time-keeper. 



I give below the results of each experiment opposite the fall (H) which 

 actuated the wheel, in revolutions per second; and I then reduce the revolu- 

 tions to what they would have been had the fall (H) been the same in every 

 experiment, having one in each series, night and day, equal to 8.41' feet. I 

 reduce R to that H by the fomula as ^ H: R=V8'41' : R'. 



DAY EXPERIMENTS. 



H Revolutions. H/ R/. 



8.410 feet, 4.901960 8.41 feet, 4.90196 



8.515 " 4.962230 " 4.93154 



8.290 " 4.889975 " 4.92524 



8.422 4.926108 " 4.92260 



8.4216 " 4.950544 " 4.94713 

 Mean revolution, 4.92569; mean temperature of water, 70.7; barometer (mean 

 height), 29.93 inches. 



NIGHT EXPERIMENTS. 



H Revolutions. H/ R/. 



8.41 feet, 4.88997 8.41 feet, 4.8S997 

 8.61 " 4.9S753 " 4.93949 



8.42 " 4.93827 " 4.93533 

 Mean revolution, 4.92159; mean temperature of water, 70.7; barometer (mean 



height), 29.91 inches. 



On comparing the results of the two series of experiments, it will be seen 

 that there was a difference of 0.00410 in favor of the wheel's revolution dur- 

 ing daytime. 



NEW APPARATUS FOR DEEP-SEA SOUNDINGS. 



The following description of a new apparatus for effecting deep-sea sound- 

 ings, devised by Lieut. Trowbridge, U. S. N., is derived from a communica- 

 tion addressed by the inventor to Prof. A. D. Bache, Superintendent Coast 

 Survey, and published in Silliman's Journal for May, 18-59 : 



"In the method of sounding hitherto employed/' says Lieut. T., "the 

 influence of the friction of the water upon the line, or ' endwise resistance,' 

 as it is called by Prof. Aiiy, was known to exist, but the amount of this end- 

 wise resistance in pounds, and its ultimate effects at great depths, had not 

 been determined. It was supposed that by making use of a weight of thirty 

 or forty pounds and a small fishing-line, this resistance would be reduced to 

 an inappreciable amount, or at least that its effect in retarding the descent of 

 the lead would not be sufficient to destroy confidence in the results." 



Lieut. T., however, claims that his own investigations prove that a weight, 

 such as is ordinarily used in sounding, will be practically held in. suspension- 



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